Electroless copper plating machine thereof, and multi-layer printed wiring board

ABSTRACT

A method is provided for removing plating blocking ions, such as anions, in pairs with copper ions and oxidant ions of a copper ion reducing agent from an electroless copper plating solution and keeping a constant salt concentration in the electroless copper plating solution during plating. The electroless copper plating method uses a plating solution containing copper sulfate as copper ion sources, and a copper ion complexing agent as copper ion sources, glyoxylic acid as a copper ion reducing agent, and a pH conditioner. The method is characterized by precipitating and removing sulfuric and oxalic ions in said electroless copper plating solution and keeping an optimum concentration of at least one of sulfuric and oxalic ions in said electroless copper plating solution during plating.

BACKGROUND OF THE INVENTION

The present invention relates to an electroless copper plating method ofreducing the concentration of byproduct ions and deposition ofbyproducts in a plating solution, a device thereof, and an applicationthereof.

The usual electroless copper plating solution contains copper ions, acopper ion complex agent, a copper ion reducing agent, and a pHconditioner, which must be supplied as the plating advances. However,this supply increases anions in pairs with copper ions, oxidant ions ofthe copper ion reducing agent, and cations of the pH conditioner in theplating solution.

These ions increasing in the plating solution will deteriorate thephysical properties of the plated layer, particularly the elongationratio of the plated layer, reducing the reliability of the plated layer.Further, it reduces the stability of the plating solution and causesabnormal deposition and autolysis.

Conventionally, to avoid such problems and to maintain a constant saltconcentration in the plating solution, various plating techniques havebeen used, such as changing plating solutions at short-time intervals,and continuously adding a new plating liquid to the plating solution inuse. However, these approaches require a large quantity of expensivecopper plating solution and a lot of labor and money to dispose ofliquid wastes.

Japanese Non-examined Patent Publication No. 56-136967 (1981) hasdisclosed a method of continuously removing such cumulative ions by anelectro dialysis. This method requires complicated operations tomaintain the optimum pH for dialysis. Further, the ion selectingmembrane which allows plating blocking ions only to penetrate themembrane is mechanically weak, difficult to maintain, and too expensive.

Japanese Non-examined Patent Publication No. 7-268638 (1995) hasdisclosed a plating method characterized by selecting the metallic ionreducing agent and the pH conditioner in the non-electro platingsolution so that the oxidant ion of the metallic ion reducing agent andthe cation of the pH conditioner may react into an insoluble salt toprevent oxidant ions of said metallic ion reducing agent from increasingin said plating solution.

However, this method is not effective to prevent an increase of anionsin pairs with metallic ions. The increase of the anions will deterioratethe plating characteristics. This method also suggests that the use ofcopper oxide or copper hydroxide in copper plating will suppresscharacteristic deterioration of the plating solution. In this case,however, the solubility of the copper oxide or copper hydroxide has agreat influence.

Solid copper oxide or copper hydroxide is usually added to the platingsolution. If the solid is not dissolved completely into the platingsolution, the particles left undissolved are plated as the cores. Thiscauses abnormal deposition or autolysis. Further, copper oxide andcopper hydroxide are more expensive than copper sulfate as copper ionsources, which is conventionally used for copper plating. That's thereason why copper oxide and copper hydroxide have not been put inpractical use.

Japanese Non-examined Patent Publication No. 7-286279 (1995) hasdisclosed a method of adding barium hydroxide to the non-electro platingsolution and removing excessive sulfuric ions as barium sulfate from theplating solution. However, this method using formalin (35% aqueousformaldehyde solution) cannot avoid a consequent increase of oxidantions of the copper ion reducing agent in the copper plating solution.The oxidant ions of the copper ion reducing agent in this method areformic ions and cannot be removed because barium formate has too great asolubility to be precipitated.

Further, this method does not blow air into the solution while addingbarium hydroxide into the plating solution. When alkaline bariumhydroxide is added to the plating solution, the pH value of the platingsolution becomes higher. In electroless copper plating, the platingsolution becomes unstable when its pH goes too high. Consequently,copper may deposit on unwanted places. This abnormal deposition onprinted circuits and the like may cause short-circuits, reducing theyield of the products. Deposition on the walls of the plating bath maydrastically deteriorate the workability.

The conventional plating equipment is usually designed to directly addcopper ions, the copper-ion reducing agent, and the pH conditioner intothe plating bath. However, this equipment cannot be free from thefloating of solid particles of insoluble salt in the plating solution.The floating solid particles when deposited on wiring boards may causeabnormal deposition on the boards.

If such a solid particle is caught in a through-hole on a printed wiringboard, it prevents part of the through-hole from being plated, causing adiscontinuity of the wiring (which is termed “through-hole void”).

In continuous electroless copper plating, byproduct ions such as anionsin pairs with copper ions and oxidant ions of the copper ion reducingagent increase in the plating solution. This increasing of the byproductions prevent the electroless copper plating reaction from forming normalplating layers and reduces the quality of the plated layer. This notonly reduces the mechanical properties of the plated layer, but alsocauses abnormal deposition of metal on unwanted locations. Up to now,there have been disclosed no effective electroless copper plating methodof preventing the increase of plating blocking ions or removing theincreased plating blocking ions and refreshing the plating solution.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a method ofremoving plating blocking ions such as anions in pairs with copper ionsand oxidant ions of the copper ion reducing agent from the electrolesscopper plating solution and keeping a constant salt concentration in theelectroless copper plating solution during plating, a device to realizesaid method, and applications thereof.

A summary of the present invention is as follows:

[1] An electroless copper plating method using a plating solutioncontaining copper sulfate as copper ion sources, and a copper ioncomplex agent, a copper ion reducing agent or glyoxylic acid as a copperion reducing agent, and pH conditioner, wherein said method comprisessteps of using the hydroxide of an alkaline earth metal as said pHconditioner to react with sulfuric ions in the electroless copperplating solution into a salt of said alkaline earth metal, removing theprecipitate from the plating solution, measuring at least one of theconcentration of sulfuric ion in the plating solution (when the copperion reducing agent is used) and the concentration of oxalic ion in theplating solution (when glyoxylic acid is used) and keeping an optimumsulfuric ion or oxalic ion concentration or preferentially 0.1 mol perliter or less of sulfuric ion and 0.2 mol per liter or less of oxalicion during plating.

[2] An electroless copper plating method using a plating solutioncontaining copper sulfate as copper ion sources, and copper ion complexagent, a copper ion reducing agent or glyoxylic acid as the copper ionreducing agent, and pH conditioner, wherein said method comprises stepsof adding at least one of alkaline earth metal, alkaline earth metaloxide, alkaline earth metal hydroxide, and alkaline earth metal salt(excluding sulfuric salt) to the plating solution to react with sulfuricions in the electroless copper plating solution into a salt of saidalkaline earth metal, removing the precipitate from the platingsolution, measuring at least one of the concentration of sulfuric ion inthe plating solution (when the copper ion reducing agent is used) andthe concentration of oxalic ion in the plating solution (when glyoxylicacid is used) and keeping an optimum sulfuric ion or oxalic ionconcentration or preferentially 0.1 mol per liter or less of sulfuricion and 0.2 mol per liter or less of oxalic ion during plating.

[3] An electroless copper plating machine using a plating solutioncontaining copper sulfate as copper ion sources, and copper ion complex,a copper ion reducing agent or glyoxylic acid as a copper ion reducingagent, and pH conditioner, wherein said device comprises an electrolesscopper plating bath, a reaction bath which adds at least one of alkalineearth metal, alkaline earth metal hydroxide, alkaline earth metal oxide,and alkaline earth metal salt (excluding sulfuric salt) to said copperplating solution therein to react with and precipitate sulfuric ions oroxalic ion (when glyoxylic acid is used) as an alkaline earth metal saltin said plating solution, a filter unit which separates said metallicsalt precipitate, means for measuring at least one of the concentrationof sulfuric ion (when the copper ion reducing agent is used) and theconcentration of oxalic ion in the plating solution (when glyoxylic acidis used), and means for comparing at least one of said measuredconcentrations by a preset reference concentration and controlling thequantity of said alkaline earth metal, alkaline earth metal hydroxide,alkaline earth metal oxide, or alkaline earth metal salt (excludingsulfuric salt) to be added.

[4] An electroless copper plating machine using a plating solutioncontaining metallic ions, an agent for reducing said metallic ions, anda pH conditioner, wherein said machine comprises An electroless copperplating bath, a reaction bath adding at least a metal or a compoundcontaining a metal to said plating solution to precipitate ions whichsuppress generation of said plating metal, and a ultrafiltration unit.

[5] Said filtration unit is preferably a cross-flow type ultrafiltrationunit or a filter press type ultrafiltration unit.

[6] A multi-layer wiring board having insulating layers and circuitlayers accumulated and cemented alternately wherein the circuit layersare electrically connected by copper-plated through-holes which passthrough the insulating layer between said circuit layers or bycopper-plated via-holes whose one end is closed and wherein the copperplating of said multi-layer wiring board is made by said electrolesscopper plating method.

[7] A module having one or more semiconductor elements on saidmulti-layer wiring board.

The method of the present invention removes said insoluble salt bysaturating it at a temperature lower than the plating temperature tocause it to precipitate and then removing the precipitate. A method ofconcentrating the plating solution can also be used to cause theinsoluble salt to precipitate.

Removal of said insoluble salt can be done by circulating the platingsolution while plating is in progress or in a batch manner when platingis not in progress after sulfuric ions and oxidant ions of the copperion reducing agent in the non-electro plating solution exceed the presetquantities.

Below will be briefly explained a copper plating using copper sulfate ascopper ion sources, as a copper ion source and glyoxylic acid as thecopper ion reducing agent.

When copper sulfate, as copper ion sources, is used as a copper ionsource, the sulfuric ions increase in the plating solution. Whenglyoxylic acid is used as a copper ion reducing agent, the glyoxylicacid behaves as glyoxalate ions in the plating solution and is reactedinto oxalic ions which are the oxidant ions. This reaction is2CHOCOO⁻+4OH⁻→2C₂O₄ ²⁻+2e⁻+2H₂O+H₂  (Reaction formula 1)

When the concentration of the byproduct ions exceeds a limit (0.1 molper liter of sulfuric ions or 0.2 mol per liter of oxalic ions), theplating solution will lose its characteristics quickly. Experimentally,the concentration of the byproduct ions exceeds the limit when a platinglayer of 30 to 60 μm thick is formed under conditions of a plating bathload of 1 dm² per liter.

When calcium hydroxide is added as a pH conditioner, the sulfuric ionsin the plating solution are precipitated as calcium sulfate and theconcentration of remaining sulfuric ions will become very low (about0.01 mol per liter or less), same the solubility of calcium sulfate isabout 0.15 gram solute per 100 grams water at 60° C.

Similarly, the oxalic ions in the plating solution are precipitated ascalcium oxalate and the concentration of remaining oxalic ions willbecome extremely low (about 7×10⁻⁶ mol per liter or less), since thesolubility of calcium oxalate is about 0.001 gram solute per 100 gramswater at 60° C. When the plating solution contains sulfuric ions of 0.01mol per liter or less and the oxalic ions of 7×10⁻⁶ mol per liter orless, the plating characteristic is excellent and the plated layer isvery ductile.

Under this condition, no abnormal copper deposition is found onnon-plating locations and the plating solution is also very stable. Toadd calcium ions into the plating solution, use a calcium pHconditioner, calcium powder, calcium acetate, calcium carbonate, calciumchloride, calcium oxide, and the like.

A similar result can be obtained when calcium is replaced by barium.When one of the above barium compounds is used, almost all sulfuric ionsin the plating solution are precipitated as barium sulfate and theconcentration of remaining sulfuric ions will become very low (about1.5×10⁻⁴ mol per liter or less), since the solubility of barium sulfateis about 0.0036 gram solute per 100 grams water at 50° C.

Similarly, the oxalic ions in the plating solution are precipitated asbarium oxalate and the concentration of remaining oxalic ions willbecome extremely low (about 7.9×10 ⁻⁵ mol per liter or less), since thesolubility of barium oxalate is about 0.00175 gram solute per 100 gramswater at 60° C.

Air must be blown into the plating solution while said compounds areadded into the plating solution to remove the precipitate of sulfuricand oxalic ions. For addition of a substance which shows alkalinity inan aqueous solution and increases the pH value of the plating solutionsuch as calcium hydroxide, barium hydroxide, calcium powder, bariumpowder, and the like, blowing air into the solution is always requiredwhile the substance is added to the plating solution.

A plating method and a plating machine in accordance with the presentinvention do not limit the choice of a complexing agent for theelectroless copper plating solution (hereinafter abbreviated as a copperplating solution). In other words, it can be any as far as it can form astable complex with copper ions such as ethylenediaminetetraacetic acid(EDTA),

-   -   Rochelle salt, nitrilotriacetic acid (NTA),    -   nitrilotripropionic acid (NTP),    -   ethylenediaminediacetic acid (EDDA),    -   ethylenediaminepropionicdihydrochloride (EDDP),    -   iminodiacetic acid (IDA),    -   trans-1.2-diaminocyclohexane-N,N,N′N′-tetraacetic acid (CyDTA),    -   diaminopropanoltetraacetic acid (DPTA-OH),    -   ethylenediaminediacetic acid (EDDA),    -   triethylenetetraaminehexaacetic acid (TTHA),    -   diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA),    -   dihydroxyethyl glycine (DHEG),    -   hydroxyethylenediaminetriacetic acid (EDTA-OH),    -   glycoletherdiaminetetraacetic acid (GEDTA),    -   nitrilotriporpionic acid (NTP),    -   diaminopropanetetraacetic acid (Methyl-EDTA)    -   hydroxyethyliminodiacetic acid (HIDA),

ethylenediaminetetraquis (methylenesulfonic acid) (EDTPO), etc. Asstated above, the sulfuric ions and the oxalic ions are precipitated andseparated as insoluble salts from the plating solution and consequentlythe plating solution can maintain optimum plating characteristics for along time. The diagram of a machine which can offer such effects isillustrated in FIG. 1.

The plating bath 1 performs electroless copper plating (hereinafterabbreviated as copper plating). The copper plating solution iscirculated along a circulation route 2 which passes through a filtercolumn 3 (for separating floating objects such as dust or solid bariumsulfate, barium oxalate, etc.). Part of the copper plating solution issent to a reaction bath 4 and receives copper ions, a copper ionreducing agent and a pH conditioner, which are lost in plating there torecover the optimum concentrations. FIG. 1 shows a heat exchanger 13 forheating the plating solution, a copper sulfate as copper ion sources, asupply tank 21, a pH conditioner supply tank 22, a copper ion reducingagent supply tank 23, and circulation pumps 24, 25, and 27.

In the reaction bath, the concentrations of copper ions, copper ionreducing agent, and pH conditioner to be added are necessarily higherthan the concentrations of those in the plating bath so as to recoverthe optimum concentrations of the plating solution in the plating bathwith the fed-back copper plating solution. If calcium hydroxide orbarium hydroxide is used as a pH conditioner, sulfuric ions and oxalicions to be removed are precipitated as insoluble salts first in thereaction bath. Further, it sometimes happens that the concentrations ofingredients of the solution in the reaction bath are high enough to makethe solution unstable.

In such a case, to prevent the copper plating solution from decomposing,a gas containing oxygen, such as air, must be blown into the reactionbath through the gas supply pipe 5. If the solubilities of sulfuricsalts and oxalic salts go lower as the liquid temperature falls, it isrecommended to cool the copper plating solution in the reaction bath toincrease the efficiency of precipitation.

In this case, the copper plating solution passing through a pre-coolingheat exchange 6 can be supplied to the reaction bath or the reactionbath itself can be cooled. Since it is desirable to heat the cooledcopper plating solution to a desired solution temperature before feedingit back to the plating bath, the copper plating solution coming from thereaction bath is fed back to the plating bath through a heating heatexchanger 7.

A concentration analyzer 8 measures the concentration of copper ions,the concentration of the reducing agent, and the pH of the platingsolution in the reaction tank. The quantities of ingredients to besupplied are controlled by pumps 9, 10, and 11 so that the measuredconcentrations may be predetermined concentrations. The concentrationsof sulfuric ions and oxalic ions can be measured by chromatography. Partof the plating solution is taken out from the reaction bath formeasurement. Besides chromatography, the measurement can be done by acapillary electrophoresis analyzer.

The copper plating solution supplied with copper ions, copper ionreducing agent, and pH conditioner from the reaction bath is fed to aultra filtration unit 12. The ultra filtration unit 12 contains an ultrafiltration membrane which separates the inner copper plating solutioncoming from the reaction bath from the outer copper plating solutioncoming from the plating bath. This is a cross-flow type ultra filtrationunit. FIG. 2 is a diagrammatic illustration of the ultra filtration unitillustrating the principle thereof. FIG. 2 shows fine particles ofcrystals 29, a cross-flow type ultra filtration unit 12, an ultrafiltration membrane 31, a flow of plating solution 32, and a filtrate33.

Using the characteristics of the ultra filtration unit that lets ionsand low molecular organic compounds penetrate the membrane, but blocksfine particles, the solid precipitate produced in the reaction bath isseparated and removed out from the system. In other words, only ionspassing through the ultra filtration membrane can be fed back to theplating bath and solid components can be continuously removed from thesystem.

In the cross-flow filtration, the copper plating solution flows alongthe surface of the membrane. This prevents the membrane from beingblocked quickly. Only the filtrate which passes through the membrane isfed back to the plating bath. This prevents the crystallized fineparticles from returning to the plating solution. The pore size of themembrane is 0.5 microns or less, preferentially 0.1 microns or less.

The filtration provided in accordance with the present invention can beany type, so long as sulfuric and oxalic salts produced in the reactionbath are not fed back to the plating bath. Preferable filtration methodsare a filter pressing method, a cross-flow method, etc.

This method enables a long stable electroless copper plating(hereinafter abbreviated as copper plating) with sulfuric and oxalic ionconcentrations low in the copper plating solution.

The purpose of the present invention can be realized with the use of asimilar method and device even when a compound which will not produceany insoluble salt, such as potassium hydroxide, etc., is used as a pHconditioner, when calcium or barium is added singly in the reaction bathor when calcium or barium carbonate, acetate, oxide, or chloride isadded to the copper plating solution.

However, when calcium carbonate and/or barium carbonate are used,carbonic ions increase in the copper plating solution. When calciumacetate and/or barium acetate are used, acetic ions increase in thecopper plating solution. Similarly, when calcium chloride and/or bariumchloride are used, chloric ions increase in the copper plating solution.

Therefore, for the use of a calcium salt and/or a barium salt, thequantity of the salt should be such that its salt precipitate may notexert any influence upon the plating characteristics. It is required toestimate the influence of the salt in advance.

On the contrary, calcium hydroxide, barium hydroxide, calcium, barium,calcium oxide, and barium oxide (when added to the copper platingsolution) will not increase ions in the copper plating solution and arepreferable since they can make the plating characteristics stable for along time period.

Potassium hydroxide can be used as a pH conditioner even when calciumhydroxide and/or barium hydroxide are used to produce oxalic or sulfuricsalt precipitate. Also, in this case, the purpose of the presentinvention can be realized.

In the above explanation, if the solubility of a compound (e.g. calciumhydroxide) to be added is low, a slurry of the compound is sometimespreferable to an aqueous solution of the compound. In this case, aslurry pump is usually used to feed the slurry compound to the reactionbath.

According to the present invention, byproduct ions, which increase as anon-electro plating reaction advances, can be eliminated, andconsequentially, the electroless copper plating solution can have alonger working life, drastically reducing the plating cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a plating machinein accordance with the present invention.

FIG. 2 is a schematic diagram of the ultra filtration unit used in theplating machine in accordance with the present invention.

FIG. 3 is a diagram illustrating the configuration of a plating machineaccording to a preferred embodiment of the present invention.

FIG. 4 is a diagram illustrating the configuration of a plating machineaccording to another preferred embodiment of the present invention.

FIG. 5 is a diagram illustrating the configuration of a plating machineaccording to another preferred embodiment of the present invention.

FIG. 6 is a schematic sectional diagram of a module having semiconductorelements on a multi-layer board plated in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

A first embodiment of the present invention uses copper sulfate ascopper ion sources, as a copper ion source, glyoxylic acid as a copperion reducing agent and barium hydroxide as a pH conditioner. Thisembodiment uses EDTA pentasodium as a complexing agent because thesolubility of barium hydroxide is not so great.

Below are listed the ingredients of the plating solution and the platingcondition.

(Ingredients) Copper (II) sulfate pentahydrate  0.04 mol per liter EDTApentasodium   0.1 mol per liter Glyoxylic acid  0.03 mol per literBarium hydroxide  0.01 mol per liter 2,2′ bipyridyl 0.0002 mol per literPolyethylene glycol  0.03 mol per liter (mean molecular weight = 600)

The concentration of barium hydroxide is controlled to keep the pH ofthe plating solution at 12.3.

(Plating Condition) pH 12.3 plating solution temperature 70° C.

A copper wiring pattern was plated on a test board in said copperplating solution. The stability of the plating solution and the qualityof the plated layer were evaluated from the existence of an abnormaldeposition of copper. The test board was prepared as stated below. Thephysical property of the plated layer was also evaluated.

(Preparation of a Test Board)

A test board was prepared by coating both surfaces of a 0.6 mm-thickglass-sheet reinforced resin laminated board with an adhesive containingacrylonitrilebutadiene rubber modified phenol resin as the mainingredient, and hardening the test board of at 160° C. for ten minutes.The hardened test board has an adhesive layer of about 30 microns thickon each surface. Then, the test board was drilled at preset locationsand dipped in a coarsening liquid containing chromic anhydride andhydrochloric acid to coarsen the adhesive surfaces.

Next, the board was dipped for ten minutes in a single-liquid palladiumcolloidal catalyst solution (fabricated by Hitachi Kasei Co., Ltd. acidaqueous solution containing intensifier HS101B) as a copper platingcatalyst, washed clean with water, and dried up at 120° C. for 20minutes.

Both surfaces of the board were coated with a dry-film photo-resistlayer 35 microns thick (SR-3000 fabricated by Hitachi Kasei Co., Ltd). Amask of a test pattern comprising lines 60 microns thick was placed onthe photo resist surface of the board. The board was exposed to lightand developed. As the result, the non-pattern parts on the surface ofthe board are all covered with the photo-resist.

The test board prepared above and a stainless steel plate were bothdipped in the plating solution at a liquid temperature of 70° C. andplated with a load of 1 dm² per liter.

The stainless steel plate was prepared by dipping the plate in 17%hydrochloric aqueous solution for 2 minutes, dipping it in the abovepalladium collidal solution for 10 minutes, and washing it thoroughly.While plating is in progress, air was blown into the plating solution tostir up the solution. A prepared liquid (listed below) was supplied tothe plating solution to make the concentration of copper ions, theconcentration of glyoxylic acid (copper ion reducing agent), and the pHconstant.

(1) Copper ion supplement (CuSO₄ 5H₂O) 200 grams

Water Quantity required to make one liter of the solution

(2) Glyoxylic acid (copper ion reducing agent) supplement 40% glyoxylicacid solution

(3) pH conditioner (Ba(OH)₂) 40 grams

Water Quantity required to make one liter of the solution

One plating cycle comprises a plating step to form a 30 μm-thick copperlayer on the stainless steel plate and the pattern area of the testboard. At the end of each plating cycle, the plated copper layer waspeeled off from the stainless steel plate, cut into a piece of 1.25 cmby 10 cm. The mechanical strength of the piece was measured by anordinary tensile tester.

The precipitates (barium sulfate, barium oxalate, and others) which wereformed during plating were filtered and removed by circulation andfiltration of the plating solution. After each plating cycle iscompleted, the plating solution is cooled down to room temperature (25°C.) and filtered to remove the precipitates (barium sulfate, bariumoxalate, and others) before the succeeding plating cycle. Theconcentrations of the sulfuric and oxalic ions in this clean platingsolution were measured by chromatography. Table 1 shows the result ofthe measurement. TABLE 1 Number of plating cycles Unit 1 2 3 4 5 6 7Embodiment 1 Conc. of sulfuric ions mol/l 8 × 10⁻³ 9 × 10⁻³ 9 × 10⁻³ 8 ×10⁻³ 8 × 10⁻³ 8 × 10⁻³ 8 × 10⁻³ Conc. of oxalic ions mol/l 7 × 10⁻⁶ 7 ×10⁻⁶ 7 × 10⁻⁶ 6 × 10⁻⁶ 7 × 10⁻⁶ 6 × 10⁻⁶ 6 × 10⁻⁶ Ductility of platefilm % 9.8 10.5 9.7 10.1 7.8 10.3 6.8 Abnormal deposition — None NoneNone None None None None Embodiment 2 Conc. of sulfuric ions mol/l 1 ×10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ Conc. ofoxalic ions mol/l 7 × 10⁻⁵ 7 × 10⁻⁵ 6 × 10⁻⁵ 7 × 10⁻⁵ 7 × 10⁻⁵ 6 × 10⁻⁵5 × 10⁻⁵ Ductility of plate film % 10.1 8.5 9.6 7.1 6.8 10.2 7.2Abnormal deposition — None None None None None None None Embodiment 3Conc. of sulfuric ions mol/l 9 × 10⁻³ 9 × 10⁻³ 8 × 10⁻³ 8 × 10⁻³ 9 ×10⁻³ 8 × 10⁻³ 8 × 10⁻³ Conc. of formic ions mol/l 0.12 0.28 0.42 0.620.78 0.92 1.12 Ductility of plate film % 10.5 8.8 7.5 6.8 5.2 4.6 3.5Abnormal deposition — None None None None None Little Little Embodiment4 Conc. of sulfuric ions mol/l 1 × 10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ 1 ×10⁻⁴ 1 × 10⁻⁴ 1 × 10⁻⁴ Conc. of formic ions mol/l 0.11 0.26 0.43 0.620.77 0.95 1.18 Ductility of plate film % 11.0 10.2 7.6 7.3 5.5 4.3 3.4Abnormal deposition — None None None None None Little Little Embodiment6 Conc. of sulfuric ions mol/l 9 × 10⁻³ 9 × 10⁻³ 9 × 10⁻³ 8 × 10⁻³ 8 ×10⁻³ 8 × 10⁻³ 8 × 10⁻³ Conc. of oxalic ions mol/l 7 × 10⁻⁶ 7 × 10⁻⁶ 7 ×10⁻⁶ 7 × 10⁻⁶ 7 × 10⁻⁶ 7 × 10⁻⁶ 7 × 10⁻⁶ Ductility of plate film % 10.28.7 9.6 8.8 8.5 9.8 7.5 Abnormal deposition — None None None None NoneNone None Comparative Conc. of sulfuric ions mol/l 0.08 0.12 0.19 0.350.55 — — embodiment 1 Conc. of formic ions mol/l 0.12 0.24 0.38 0.670.98 — — Ductility of plate film % 9.8 7.5 5.4 3.2 1.2 — — Abnormaldeposition — None Little Some Some Deposition — — Comparative Conc. ofsulfuric ions mol/l 0.08 0.13 0.18 0.33 0.56 — — embodiment 2 Conc. ofoxalic ions mol/l 0.12 0.24 0.37 0.77 1.02 — — Ductility of plate film %9.7 7.7 5.2 2.8 1.0 — — Abnormal deposition — None Little Some SomeDeposition — —

The concentrations of sulfuric and oxalic ions in the plating solutionwere measured after the plating solution was filtered at the end of eachplating cycle.

Even after seven plating cycles, the sulfuric ion concentration was1.5×10⁻⁴ mol per liter or less and the oxalic ion concentration was7.9×10⁻⁵ mol per liter or less. The ductility of the obtained platedlayer was 6% or more and was not deteriorated so much as the number ofplating cycles increased. Further, no abnormal deposition was visuallydetected on the test board, in the plating bath, pipings, and so on. Theplating solution was extremely steady even after seven plating cycleswere completed.

As stated above, the method in accordance with the present invention wasfound to suppress an increase of sulfuric and oxalic ions in the platingsolution. This is due to the use of barium hydroxide as a pH conditionerwhich causes the sulfuric and oxalic ions to precipitate as insolublebarium salts. This precipitate is separated from the plating solution,and so the plating solution can be almost free from sulfuric and oxalicions.

The long excellent plating characteristics can be obtained by platingunder conditions of the sulfuric ion concentration of 0.1 mol per literor less and the oxalic ion concentration of 0.2 mol per liter or less inthe plating solution.

Embodiment 2

A second embodiment of the present invention was carried out under thesame conditions as the first embodiment, but barium hydroxide as a pHconditioner was substituted by calcium hydroxide. As the solubility ofcalcium hydroxide is very low (approx. 1.7 gram solute per 1 literwater), its aqueous solution is not available. Therefore calciumhydroxide in slurry (obtained by powering calcium hydroxide and addingpure water thereto) was used.

Powdered calcium hydroxide has greater surfaces in contact with theplating solution and can easily react with sulfuric and oxalic ions intoinsoluble precipitates in the plating solution although the solubilityof calcium hydroxide is very low. In this case, however, the efficiencyof removal of sulfuric and oxalic ions from the plating solution isdependent upon the granule sizes of the calcium hydroxide powder, therate of solution stirring, and so on. They must be optimized in advance.

To prevent a lot of crystals including undissolved calcium hydroxidefrom existing in the plating solution, this embodiment employs a methodof adding a slurry of calcium hydroxide into the reaction bath, which isprovided separately from the plating bath, instead of adding a slurry ofcalcium hydroxide directly into the plating bath, mixing the slurry andthe plating solution in the plating bath, removing the precipitate bythe ultra filtration unit, and feeding back the filtered platingsolution to the plating bath.

Table 1 shows the result of an evaluation of the platingcharacteristics. This method can keep the sulfuric and oxalicconcentrations very low (0.01 mol per liter or less of sulfuric ion and7×10⁻⁶ mol per liter or less of oxalic ion) even after seven platingcycles.

The ductility of the obtained copper layer (foil) was 6% or more andremained almost unchanged even after many plating cycles. Further, noabnormal deposition was visually detected on the test board, in theplating bath, pipings, and so on. The plating solution was extremelysteady even after seven plating cycles were completed.

Embodiment 3

A third embodiment of the present invention uses copper sulfate ascopper ion sources, as a copper ion source, formaldehyde as a copper ionreducing agent and barium hydroxide as a pH conditioner. In this case,the oxidant ion of the formaldehyde is formic acid. This embodimentassumes that formic acid cannot be removed as a precipitate. Below arelisted the ingredients of the plating solution and the platingcondition.

(Ingredients) Copper (II) sulfate pentahydrate  0.04 mol per liter EDTApentasodium   0.1 mol per liter Formaldehyde  0.03 mol per liter Bariumhydroxide  0.01 mol per liter 2,2′ bipyridyl 0.0002 mol per literPolyethylene glycol  0.03 mol per liter (mean molecular weight = 600)

The concentration of barium hydroxide is controlled to keep the pH ofthe plating solution at 12.3.

(Plating Condition) pH 12.3 Liquid temperature 70° C.

This embodiment plated the same test board using the same method asEmbodiment 1 in the above copper plating solution. The physical propertyof the obtained plated layer (foil), abnormal deposition, andconcentrations of salts in the plating solution were tested and measuredin the same manner as Embodiment 1. 37% formaldehyde aqueous solution isused to supply the copper ion reducing agent.

Table 1 shows the result of an evaluation of the platingcharacteristics. The concentration of sulfuric ions in the platingsolution was measured after the plating solution was filtered at the endof each plating cycle. This method can keep the sulfuric concentrationvery low (1.5×10⁻⁴ mol per liter or less) even after seven platingcycles.

The ductility of the plated layer (foil) formed in the seventh platingcycle was under half as much as that of the plated layer (foil) formedin the first plating cycle, but it was strong enough to assure thereliability. Further, within five plating cycles, no abnormal depositionwas visually detected on the test board, in the plating bath, pipings,and so on. The plating solution was extremely steady. After the sixthand seventh plating cycles, a little abnormal deposition was found onthe test board and in the plating bath, but it was not significantenough to cause short-circuiting of a wiring pattern on the test board.

Embodiment 4

A fourth embodiment of the present invention was carried out under thesame conditions as the third embodiment, but the pH conditioner for theplating solution and the supplement was calcium hydroxide. As thesolubility of calcium hydroxide is very low, its aqueous solution is notavailable. Therefore calcium hydroxide (in slurry) was used as in thesecond embodiment.

The result of measurement is listed in Table 1. This method can keep thesulfuric concentration very low (0.01 mol per liter or less) after theseven plating cycles. The ductility of the plated layer (foil) formed inthe seventh plating cycle was under half as much as that of the platedlayer (foil) formed in the first plating cycle, but it was strong enoughto assure the required reliability.

Further, within five plating cycles, no abnormal deposition was visuallydetected on the test board, in the plating bath, pipings, and so on. Theplating solution was extremely steady. After the sixth and seventhplating cycles, a little abnormal deposition was found on the test boardand in the plating bath, but it was not significant enough to causeshort-circuiting of a wiring pattern on the test board.

Embodiment 5

A copper plating solution of a fifth embodiment of the present inventionwas prepared using copper sulfate as copper ion sources, as a copper ionsource, glyoxylic acid as a copper ion reducing agent and potassiumhydroxide as a pH conditioner in preparation of a plating solution.

(Ingredients) Copper (II) sulfate pentahydrate  0.04 mol per liter EDTApentasodium   0.1 mol per liter Glyoxylic acid  0.03 mol per literPotassium hydroxide  0.03 mol per liter 2,2′ bipyridyl 0.0002 mol perliter Polyethylene glycol  0.03 mol per liter (mean molecular weight =600)

The concentration of potassium hydroxide is controlled to keep the pH ofthe plating solution at 12.3.

(Plating Condition) pH 12.3 Liquid temperature 70° C.

A prepared liquid (listed below) was supplied to the plating solution tomake the concentration of copper ions, the concentration of glyoxylicacid (a copper ion reducing agent), and the pH constant, although theydecrease as the plating advances.

(1) Copper ion supplement (CuSO₄ 5H₂O) 200 grams

Water Quantity required to make one liter of the solution

(2) Glyoxylic acid (copper ion reducing agent) supplement 40% glyoxylicacid solution

(3) pH conditioner (Ba(OH)₂) 40 grams

Water Quantity required to make one liter of the solution

As seen from the above, an aqueous solution of barium hydroxide is usedto keep the pH of the plating solution constant, although potassiumhydroxide is used as a pH conditioner when the plating solution isprepared.

Even after seven plating cycles, the sulfuric ion concentration was1.5×10⁻⁴ mol per liter or less and the oxalic ion concentration was7.9×10⁻⁵ mol per liter or less. The ductility of the obtained platedlayer was 6% or more and was not deteriorated so much as the number ofplating cycles increased. Further, no abnormal deposition was visuallydetected on the test board, in the plating bath, pipings, and so on. Theplating solution was extremely steady even after seven plating cycleswere completed.

Embodiment 6

A sixth embodiment of the present invention uses a plating solutioncontaining copper sulfate as copper ion sources, as a copper ion source,glyoxylic acid as a copper ion reducing agent and potassium hydroxide asa pH conditioner. Below are listed the ingredients of the platingsolution and the plating condition.

(Ingredients) Copper (II) sulfate pentahydrate  0.04 mol per liter EDTApentasodium   0.1 mol per liter Glyoxylic acid  0.03 mol per literPotassium hydroxide  0.03 mol per liter 2,2′ bipyridyl 0.0002 mol perliter Polyethylene glycol  0.03 mol per liter (mean molecular weight =600)

The concentration of potassium hydroxide is controlled to keep the pH ofthe plating solution at 12.3.

(Plating Condition) pH 12.3 Liquid temperature 70° C.

This embodiment carried out plating according to the processing flowillustrated in FIG. 1 using the above plating solution. In other words,the copper plating was carried out in the plating bath 1. The platingsolution is circulated through a filtration column 3 along thecirculation path 2.

Part of the copper plating solution is sent to a reaction bath 4 andreceives copper ions, a copper ion reducing agent, and a pH conditionerto supplement the lost quantities of ingredients. The composition of thesupplemental solution is listed below.

(1) Copper ion supplement (CuSO₄.5H₂O) 200 grams

Water Quantity required to make one liter of the solution

(2) Glyoxylic acid (copper ion reducing agent) supplement 40% glyoxylicacid solution

(3) pH conditioner (KOH) 200 grams

Water Quantity required to make one liter of the solution

Calcium powder was added to the plating solution in the reaction bath toreact with sulfuric and oxalic ions into insoluble salts. As the pH ofthe plating solution increases when the calcium powder is added, the pHconditioner is added to the plating solution to decrease the pH.Further, the calcium powder generates heat of dissolution when itdissolves into the plating solution. Thus, care must be taken whendissolving the powder.

Therefore, the reaction bath was cooled for efficient separation of theprecipitate of oxalic salt.

When the calcium powder is added, the plating solution has lots ofprecipitates (calcium sulfate, calcium oxalate, and calcium particleswhich remain un-dissolved). Embodiment 6 removed these precipitates fromthe plating solution by means of the ultra filtration unit, regulatedthe concentration of copper ions, the concentration of glyoxylic acidand the pH to predetermined values, and then fed back the platingsolution to the plating bath 1.

Table 1 shows the result of an evaluation of the plating characteristics(the concentration of sulfuric ions, the concentration of oxalic ions,the ductility of the plated layer, and detection of abnormal deposition)of each plating cycle.

The concentration of sulfuric ions and the concentration of oxalic ionsin the table are the result of measurement after each plating cycle iscompleted. This embodiment can keep the sulfuric and oxalicconcentrations very low (0.01 mol per liter or less of sulfuric ion and7×10⁻⁶ mol per liter or less of oxalic ion) even after seven platingcycles.

The ductility of the obtained copper layer (foil) was 6% or more andremained almost unchanged even after many plating cycles. Further, noabnormal deposition was visually detected on the test board, in theplating bath, pipings, and so on. The plating solution was extremelysteady even after seven plating cycles were completed.

Embodiment 7

A seventh embodiment of the present invention was carried out under thesame conditions as Embodiment 6, but calcium powder was replaced bybarium oxide to react with sulfuric and oxalic ions into precipitates.The testing method of this embodiment is the same as Embodiment 6.

This embodiment can keep the sulfuric and oxalic concentrations very low(1.5×10⁻⁴ mol per liter or less of sulfuric ion and 7.9×10⁻⁵ mol perliter or less of oxalic ion) even after seven plating cycles. Theductility of the obtained copper layer (foil) was 6% or more andremained almost unchanged even after many plating cycles. Further, noabnormal deposition was visually detected on the test board, in theplating bath, pipings, and so on. The plating solution was extremelysteady even after seven plating cycles were completed.

Embodiment 8

An eighth embodiment of the present invention was carried out under thesame conditions as Embodiment 6, but calcium powder was replaced bybarium carbonate to react with sulfuric and oxalic ions intoprecipitates. The testing method of this embodiment is the same asEmbodiment 6.

This embodiment can keep the sulfuric and oxalic concentrations very low(1.5×10⁻⁴ mol per liter or less of sulfuric ion and 7.9 ? 10−5 mol perliter or less of oxalic ion) even after seven plating cycles. Theductility of the obtained copper layer (foil) was 6% or more andremained almost unchanged even after many plating cycles.

However, it was found that the plating rate was reduced as the carbonateincreased in the plating solution. As a result of visual checks, theplating solution was extremely steady even after seven plating cycleswere completed, but a little abnormal deposition was found on the testboard.

As stated above, the most excellent barium compound to be added to theplating solution to react with sulfuric and oxalic ions intoprecipitates is barium oxide, barium hydroxide, or a simple substance ofbarium, since they will not increase ions in the plating solution.

Although barium carbonate added to the plating solution as in thisembodiment can suppress an increase of sulfuric and oxalic ions in theplating solution, an increase of carbonate ions was recognized. However,the plating characteristic of this embodiment is better than that of amethod which does not use this embodiment. By plating with aconcentration of sulfuric ions of 0.1 mol per liter and a concentrationof oxalic ions of 0.2 mol per liter in the plating solution, anexcellent plating characteristic can be maintained for a long time. Thisis the effect of this embodiment.

Embodiment 9

A ninth embodiment of the present invention was carried out under thesame conditions as Embodiment 6, but calcium powder was replaced bybarium acetate to react with sulfuric and oxalic ions into precipitates.The testing method of this embodiment is the same as Embodiment 6.

This embodiment can keep the sulfuric and oxalic concentrations very low(1.5×10⁻⁴ mol per liter or less of sulfuric ion and 7.9×10⁻⁵ mol perliter or less of oxalic ion) even after seven plating cycles. Theductility of the obtained copper layer (foil) was 3% or more and alittle inferior to that of the embodiment using barium hydroxide. As aresult of visual checks, the plating solution was extremely steady evenafter seven plating cycles were completed, but a little abnormaldeposition was found on the test board. It is assumed that this iscaused by the increase of acetic ions in the plating solution.

Although barium acetate added to the plating solution as in thisembodiment can suppress an increase of sulfuric and oxalic ions in theplating solution, an increase of acetate ions was recognized. However,the plating characteristic of this embodiment is better than that of amethod which does not use this embodiment. By plating with aconcentration of sulfuric ions of 0.1 mol per liter and a concentrationof oxalic ions of 0.2 mol per liter in the plating solution, anexcellent plating characteristic can be maintained for a long time.

Embodiment 10

A tenth embodiment of the present invention was carried out under thesame conditions as Embodiment 6, but calcium powder was replaced bybarium chloride to react with sulfuric and oxalic ions intoprecipitates. The testing method of this embodiment is the same asEmbodiment 6.

This embodiment can keep the sulfuric and oxalic concentrations very low(1.5×10⁻⁴ mol per liter or less of sulfuric ion and 7.9×10⁻⁵ mol perliter or less of oxalic ion) even after seven plating cycles. Theductility of the obtained copper layer (foil) was 3% or more and alittle inferior to that of the embodiment using barium hydroxide. As aresult of visual checks, the plating solution was extremely steady evenafter seven plating cycles were completed, but a little abnormaldeposition was found on the test board. It is assumed that this iscaused by the increase of chloric ions in the plating solution.

As stated above, the most excellent barium compound to be added to theplating solution to react with sulfuric and oxalic ions intoprecipitates is barium hydroxide, barium oxide, or a simple substance ofbarium, since they will not increase ions in the plating solution.

Although barium chloride added to the plating solution as in thisembodiment can suppress an increase of sulfuric and oxalic ions in theplating solution, an increase of chloride ions was recognized. However,the plating characteristic of this embodiment is better than that of amethod which does not use this embodiment. By plating with aconcentration of sulfuric ions of 0.1 mol per liter and a concentrationof oxalic ions of 0.2 mol per liter in the plating solution, anexcellent plating characteristic can be maintained for a long time. Thisis the effect of this embodiment.

Embodiment 11

This embodiment of the present invention was carried out under the sameconditions as Embodiment 6, but calcium to be added to the platingsolution was replaced by barium to react with sulfuric and oxalic ionsinto precipitates.

This embodiment can keep the sulfuric and oxalic concentrations very low(1.5×10⁻⁴ mol per liter or less of sulfuric ion and 7.9×10⁻⁵ mol perliter or less of oxalic ion) even after seven plating cycles. Theductility of the obtained copper layer (foil) was 6% or more andremained almost unchanged even after many plating cycles. Further, noabnormal deposition was visually detected on the test board, in theplating bath, pipings, and so on. The plating solution was extremelysteady even after seven plating cycles were completed.

Embodiment 12

A twelfth embodiment of the present invention uses copper sulfate ascopper ion sources, as a copper ion source, formaldehyde as a copper ionreducing agent and potassium hydroxide as a pH conditioner. In thiscase, the oxidant ion of the formaldehyde is formic acid. Thisembodiment assumes that formic acid cannot be removed as a precipitate.Below are listed the ingredients of the plating solution and the platingcondition.

(Ingredients) Copper (II) sulfate pentahydrate  0.04 mol per liter EDTApentasodium   0.1 mol per liter Formaldehyde  0.03 mol per literPotassium hydroxide  0.03 mol per liter 2,2′ bipyridyl 0.0002 mol perliter Polyethylene glycol  0.03 mol per liter (mean molecular weight =600)

The concentration of potassium hydroxide is controlled to keep the pH ofthe plating solution at 12.3.

(Plating Condition) pH 12.3 Liquid temperature 70° C.

This embodiment plated the same test board using the same method asEmbodiment 1 in the above copper plating solution in the plating flowillustrated in FIG. 1.

The copper plating solution is circulated along a circulation route 2which passes through a filter column 3.

Part of the copper plating solution is sent to a reaction bath 4 andreceives copper ions, a copper ion reducing agent, and a pH conditioner,which are lost in plating there, to recover the optimum concentrations.The composition of the supplemental solution is listed below.

(1) Copper ion supplement (CuSO₄.5H₂O) 200 grams

Water Quantity required to make one liter of the solution

(2) Formaldehyde (copper ion reducing agent) supplement 37% glyoxylicacid solution.

(3) pH conditioner (KOH) 200 grams

Water Quantity required to make one liter of the solution.

Calcium powder was added to the plating solution in the reaction bath toreact with sulfuric ions into insoluble salt. As the pH of the platingsolution increases when the calcium powder is added, the pH conditionerwas added to the plating solution to decrease the pH. Further, thecalcium powder generates a lot of heat of dissolution when it dissolvesinto the plating solution. Thus, care must be taken when dissolving thepowder. Therefore, the reaction bath was cooled for efficient separationof the precipitate of oxalic salt.

When the calcium powder is added, the plating solution has lots ofprecipitates (calcium sulfate and calcium particles which remainundissolved). This embodiment removed these precipitates from theplating solution by means of the ultra filtration unit, regulated theconcentration of copper ions, the concentration of formaldehyde and thepH to predetermined values, and then fed back the plating solution tothe plating bath 1.

This embodiment can keep the sulfuric concentration very low (1.5×10⁻⁴mol per liter or less) even after seven plating cycles. The ductility ofthe plated layer (foil) formed in the seventh plating cycle was 3% whichis under half as much as that of the plated layer (foil) formed in thefirst plating cycle, but it was strong enough to assure the reliability.

Further, within five plating cycles, no abnormal deposition was visuallydetected on the test board, in the plating bath, pipings, and so on. Theplating solution was extremely steady. After the sixth and seventhplating cycles, a little abnormal deposition was found on the test boardand in the plating bath, but it was not significant enough to causeshort-circuiting of a wiring pattern on the test board.

Comparative Embodiment 1

This embodiment performed copper plating using a conventional copperplating solution which contained formaldehyde as a copper ion reducingagent and sodium hydroxide as a pH conditioner.

The pH and the temperature of the plating solution were respectively12.5 and 70° C. In this case, the oxidant ion of the formaldehyde isformic acid and the solubility of sodium formate is extremely high (99.6grams solute per 100 grams water at 25° C.). Further, the solubility ofsodium sulfate is also high (21.9 grams solute per 100 grams water at25° C.). Therefore, sodium formate and sodium sulfate will neverprecipitate even after the copper plating solution is cooled, and sothese ions (byproduct ions) cannot be removed.

The concentration of sulfuric ions, the concentration of formic ions,and the physical quantity of the plated layer (foil) in repetitiveplating are illustrated in Table 1.

Table 1 shows that, as the repetitive plating advances, the sulfuric andformic ions increase in the plating solution and the ductility of theplated layer (foil) decreases. Further, the copper plating solutionbecame unstable as the plating advanced. The plating solution startedautolysis halfway in the fifth plating and was unable to plate.

Comparative Embodiment 2

This embodiment performed copper plating using the same copper platingsolution as Comparative Embodiment 2 but calcium hydroxide as the pHconditioner was replaced by potassium hydroxide. The pH and thetemperature of the plating solution were respectively 12.5 and 70° C.

In this case, the solubility of potassium sulfate is high (10.8 gramssolute per 100 grams water at 25° C.). Therefore, sodium sulfate willnever precipitate, and so the sulfuric ions cannot be removed.

Similarly, the solubility of potassium oxalate is also high (35.9 gramssolute per 100 grams water at 25° C.). Therefore, potassium oxalate didnot precipitate even after the copper plating solution was cooled, andso the oxalic ions could not be removed.

The concentration of sulfuric ions, the concentration of oxalic ions,and the physical quantity of the plated layer (foil) in repetitiveplating are illustrated in Table 1.

Table 1 shows that, as the repetitive plating advances, the amount ofsulfuric and oxalic ions increases in the plating solution and theductility of the plated layer (foil) decreases. Further, the copperplating solution became unstable as the plating advanced. The platingsolution started autolysis halfway in the fifth plating and was unableto plate.

As seen from the above, it is apparatus that use methods which are notin accordance with the present invention that cause blocking ions toincrease in the plating solution, with the result that the platingcharacteristics are deteriorated. This has proven that the presentinvention has an advantage.

Embodiment 13

Below will be explained a plating machine which is one embodiment inaccordance with the present invention. FIG. 3 is a diagram showing theconfiguration of a plating machine in accordance with the presentinvention.

The copper plating was carried out in the plating bath 1. The copperplating solution is circulated through a filtration column 3 along acirculation path 2 to remove solids floating in the copper platingsolution. The device has another circulation path passing through a heatexchanger 13 to heat up the copper plating solution to a predeterminedtemperature.

Part of the copper plating solution is sent to a reaction bath 4 andreceives copper ions, a copper ion reducing agent, and a pH conditionerto supplement the lost quantities of ingredients.

In the reaction bath 4, the concentrations of copper ions, copper ionreducing agent, and pH conditioner to be added are necessarily higherthan the concentrations of those in the plating bath to recover theoptimum concentrations of the plating solution in the plating bath 1with the fed-back copper plating solution.

To prevent the copper plating solution from decomposing in the reactionbath 4, a gas containing oxygen, such as air, is blown into the copperplating solution in the reaction bath through a gas supply valve 5 tostir up the solution with the gas. A concentration analyzer 8 measuresthe concentration of copper ions, the concentration of the reducingagent, and the pH of the plating solution in the reaction tank. Thequantities of ingredients to be supplied are controlled by pumps 9, 10,and 11 so that the measured concentrations may be predeterminedconcentrations.

Pumps 9, 10, and 11 respectively supply copper sulfate as copper ionsources, aqueous solution, glyoxylic acid aqueous solution, and bariumhydroxide aqueous solution in that order.

The concentrations of copper ions, the copper ion reducing agent, andthe pH conditioner of the copper plating solution in the reaction bathare higher than those of the plating solution in the plating bath.Barium sulfate and barium oxalate are saturated and precipitated firstin the reaction bath 4 as the copper plating solution is cooled by theheat exchanger 6 before entering the reaction bath 4.

These precipitates (fine crystallized particles) are separated from thecopper plating solution by the cross-flow type ultra filtration unit 12.The filtered clean copper plating solution is fed back to the platingbath through the heating heat exchanger 7.

The copper plating solution containing a lot of precipitate is sent tothe settling bath 14 in the upstream side of the reaction bath 4. Onlythe supernatant plating solution overflows a weir which is providedbetween the settling bath 14 and the reaction bath 4 back into thereaction bath 4.

70% or more of the solid precipitate in the copper plating solution sentto the settling bath 14 remains settled and is taken out of the system.

As stated above, the device in accordance with the present invention canremove sulfuric and oxalic ions which deteriorate the platingcharacteristics as barium salts and maintain an excellent platingcharacteristic for a long time.

Embodiment 14

FIG. 4 is a flow diagram of a plating machine using a filter press typeultra filtration unit. This embodiment uses almost the same units asthose of Embodiment 13 and performs similar operations. An explanationthereof is omitted here. Unit 17 is a recovery tank.

This embodiment is characterized in that the whole reaction bath 4 iscooled further by water sent from the cooling unit 15 after part of thecopper plating solution is supplied to the reaction bath 4.

The concentrations of copper ions, the copper ion reducing agent, andthe pH conditioner of the copper plating solution in the reaction bath 4are higher than those of the plating solution in the plating bath 1, andthe reaction bath 4 is cooled by water from the cooling unit 15.Therefore, barium sulfate and barium oxalate are first saturated andeasily precipitated in the reaction bath.

These precipitates (fine crystallized particles) are separated from thecopper plating solution by the filter press type ultra filtration unit16. The filtered clean copper plating solution is fed back to theplating bath 1 through the heating heat exchanger 7.

The precipitate caught by the filter press type ultra filtration unit 16is scaled off from the filter membrane into the recovery tank 17 througha funnel-shaped collecting means, and taken out from the system.

As stated above, the device in accordance with the present invention canremove sulfuric and oxalic ions which deteriorate the platingcharacteristics as barium salts and maintain an excellent platingcharacteristic for a long time.

Embodiment 15

This embodiment uses a copper plating solution containing bariumhydroxide or calcium hydroxide as a pH conditioner. FIG. 5 is a flowdiagram of a plating machine using alkaline metal hydroxide such assodium hydroxide or potassium hydroxide as a pH conditioner. FIG. 5contains a delivery pump 26 and an alkali earth metal salt supply tank28.

The reaction bath 4 is equipped with a supply pump 18 for supplyingaqueous solution containing at least one of calcium hydroxide, bariumhydroxide, calcium carbonate, barium carbonate, calcium acetate, bariumacetate, calcium oxide, barium oxide, calcium, and barium to react withsulfuric and oxalic ions into precipitates.

The quantities of chemicals to precipitate the ions are regulated by apump 9 for supplying copper sulfate as copper ion sources, aqueoussolution, a pump 10 for supplying glyoxylic acid aqueous solution, andan analyzing unit 8.

The quantity of sulfuric ions in the copper plating solution can becalculated from the quantity of copper sulfate as copper ion sources,solution supplied by pump 9. The quantity of oxalic ions in the copperplating solution is calculated as the difference between the quantity ofoxalic acid solution measured by the analyzing unit 8 and the quantityof the existing glyoxylic acid. The copper plating solution control unit19 performs these calculations and controls the pump 18 according to theresult of calculation. The other configuration of this embodiment is thesame as that of Embodiment 13 and Embodiment 14.

As stated above, the device in accordance with the present invention canremove sulfuric and oxalic ions which deteriorate the platingcharacteristics as barium salts and maintain an excellent platingcharacteristic for a long time.

Embodiment 16

FIG. 6 is a diagrammatic sectional view of a module comprising amulti-layer wiring board 54 produced by a copper plating method inaccordance with the present invention and semiconductor elementsthereon. A number 45 indicates an insulating layer.

The multi-layer wiring board 54 is prepared by forming a wiring patternon each board with a known photo-resist, plating a conductor wiring 34on the board by a method stated in said embodiments, and piling a presetnumber of said plated boards with an insulating layer 37 therebetween.

The conductor wirings on the plated boards are electrically connected byvia-holes 36 and through-holes 35 which are drilled in advance andplated by a copper plating method of the present invention.

Semiconductor elements 46 are mounted on predetermined locations of saidmulti-layer wiring board 54 by a method using solder balls 44. Withthis, a highly reliable module can be obtained.

1. An electroless copper plating method using a plating solutioncontaining copper sulfate as copper ion sources, and a copper ioncomplex agent, a copper ion reducing agent and a pH conditioner, whereinsaid method comprises steps of using the hydroxide of an alkaline earthmetal as said pH conditioner to react with sulfuric ions in theelectroless copper plating solution into a salt of said alkaline earthmetal, removing the precipitate from the plating solution, measuring atleast one of the concentration of sulfuric ion and the concentration ofoxalic ion in the plating solution and keeping an optimum sulfuric ionor oxalic ion concentration during an electroless copper plating.
 2. Anelectroless copper plating method using a plating solution containingcopper sulfate as copper ion sources, and a copper ion complex agent,glyoxylic acid or salt thereof as a copper ion reducing agent, and pHconditioner, wherein said method comprises steps of using alkaline earthmetal hydroxide as said pH conditioner, precipitating and removingsulfuric and oxalic ions as salts of said alkaline earth metal in theelectroless plating solution during electroless copper plating.
 3. Anelectroless copper plating method using a plating solution containingcopper sulfate as copper ion sources, and a copper ion complex agent, acopper ion reducing agent, and a pH conditioner, wherein said methodcomprises steps of adding at least one of alkaline earth metal, alkalineearth metal oxide, alkaline earth metal hydroxide, and alkaline earthmetal salt (excluding sulfuric salt) into said plating solution,reacting with and precipitating sulfuric ions as an alkaline earth metalsalt, measuring the concentration of sulfuric ions in said platingsolution, and regulating the concentration thereof to a preset optimumconcentration during electroless copper plating.
 4. An electrolesscopper plating method using a plating solution containing copper sulfateas copper ion sources, and a copper ion complex agent, glyoxylic acid orsalt thereof as a copper ion reducing agent, and a pH conditioner,wherein said method comprises steps of adding at least one of alkalineearth metal, alkaline earth metal oxide, alkaline earth metal hydroxide,and alkaline earth metal salt (excluding sulfuric salt) into saidplating solution, and reacting with and precipitating sulfuric ions oroxalic ion as an alkaline earth metal salt during electroless copperplating.
 5. An electroless copper plating machine using a platingsolution containing metallic ions, an agent for reducing said metallicions, and a pH conditioner, wherein said machine comprises anelectroless copper plating bath, a reaction bath adding a metal or acompound containing a metal to said plating solution to precipitateions, as a metal salt precipitate, which suppress generation of saidplating metal as metal salts, and an ultra filtration unit for removingsaid metal salt precipitate.
 6. A multi-layer wiring board havinginsulating layers and circuit layers accumulated and cementedalternately whose circuit layers are electrically connected bycopper-plated through-holes which pass through the insulating layerbetween said circuit layers or by copper-plated via-holes whose one endis closed, wherein said plating is made by an electroless copper platingmethod in accordance with claim
 1. 7. A module having one or moresemiconductor elements on said multi-layer wiring board in accordancewith claim
 6. 8. A multi-layer wiring board having insulating layers andcircuit layers accumulated and cemented alternately whose circuit layersare electrically connected by copper-plated through-holes which passthrough the insulating layer between said circuit layers or bycopper-plated via-holes whose one end is closed, wherein said plating ismade by an electroless copper plating method in accordance with claim 2.9. A module having one or more semiconductor elements on saidmulti-layer wiring board in accordance with claim
 8. 10. A multi-layerwiring board having insulating layers and circuit layers accumulated andcemented alternately whose circuit layers are electrically connected bycopper-plated through-holes which pass through the insulating layerbetween said circuit layers or by copper-plated via-holes whose one endis closed, wherein said plating is made by an electroless copper platingmethod in accordance with claim
 3. 11. A module having one or moresemiconductor elements on said multi-layer wiring board in accordancewith claim
 10. 12. A multi-layer wiring board having insulating layersand circuit layers accumulated and cemented alternately whose circuitlayers are electrically connected by copper-plated through-holes whichpass through the insulating layer between said circuit layers or bycopper-plated via-holes whose one end is closed, wherein said plating ismade by an electroless copper plating method in accordance with claim 4.13. A module having one or more semiconductor elements on saidmulti-layer wiring board in accordance with claim 12.